Added a "canInject" property in the injectors.

ProtocolLib/src/com/comphenix/protocol/injector/NetworkFieldInjector.java

@@ -83,6 +83,13 @@ class NetworkFieldInjector extends PlayerInjector {
 		}
 	}
 	
+
+	@Override
+	public boolean canInject() {
+		// Probably
+		return true;
+	}
+	
 	@Override
 	public void injectManager() {
 		

ProtocolLib/src/com/comphenix/protocol/injector/NetworkObjectInjector.java

@@ -42,6 +42,14 @@ class NetworkObjectInjector extends PlayerInjector {
 		}
 	}
 	
+	@Override
+	public boolean canInject() {
+		// We only support 1.3.0 at the moment. Fixing it require us to
+		// add jMock, which would add another dependency.
+		return networkManager != null && 
+			   networkManagerField.getType().isInterface();
+	}
+	
 	@Override
 	public void injectManager() {
 		

ProtocolLib/src/com/comphenix/protocol/injector/PacketFilterManager.java

@@ -67,7 +67,7 @@ public final class PacketFilterManager implements ProtocolManager {
 		/**
 		 * Override the network handler object itself.
 		 */
-		NETWORK_MANAGER_OBJECT
+		NETWORK_MANAGER_OBJECT,
 	}
 	
 	// Create a concurrent set
@@ -362,16 +362,20 @@ public final class PacketFilterManager implements ProtocolManager {
 	 * @throws IllegalAccessException Unable to do our reflection magic.
 	 */
 	protected PlayerInjector getPlayerHookInstance(Player player) throws IllegalAccessException {
-		
+		return getHookInstance(player, playerHook);
+	}
+	
+	// Helper
+	private PlayerInjector getHookInstance(Player player, PlayerInjectHooks hook) throws IllegalAccessException {
 		// Construct the correct player hook
-		switch (playerHook) {
+		switch (hook) {
 		case NETWORK_HANDLER_FIELDS: 
 			return new NetworkFieldInjector(player, this, sendingFilters);
 		case NETWORK_MANAGER_OBJECT: 
 			return new NetworkObjectInjector(player, this, sendingFilters);
+		default:
+			throw new IllegalArgumentException("Cannot construct a player injector.");
 		}
-		
-		throw new IllegalArgumentException("Cannot construct a player injector.");
 	}
 	
 	/**

ProtocolLib/src/com/comphenix/protocol/injector/PlayerInjector.java

@@ -190,6 +190,12 @@ abstract class PlayerInjector {
 	 */
 	public abstract void cleanupAll();
 	
+	/**
+	 * Determine if we actually can inject.
+	 * @return TRUE if this injector is compatible with the current CraftBukkit version, FALSE otherwise.
+	 */
+	public abstract boolean canInject();
+	
 	/**
 	 * Allows a packet to be recieved by the listeners.
 	 * @param packet - packet to recieve.